Seletividade de herbicidas e dinâmica populacional de plantas daninhas na cultura do girassol para a produção de biodiesel

Experiments were conducted in Prudente de Morais County, Minas Gerais State, in 2010 and 2011 years, with the objective of to evaluate selectivity and efficiency of pre and post-emergence herbicides in sunflower crop, as well as to study weeds populacional dynamic. The work conducted in 2010 was carried out in greenhouse, in a randomized complete block design, with 11 treatments and three replications. Treatments consisted by ten herbicides, four in pre emergence and six in post-emergent of the crop (alachlor, imazaquin, metribuzin, trifluralin, chlorimuron-ethyl, fenoxaprop-p-ethyl, [fluazifop-p + fomesafen], imazapyr, imazethapyr e sethoxydim) and a check. The following characteristics were evaluated: phytotoxicity effects, plants height, leaves number and dry biomass of shoot and root 60 days after product applications. In 2011, the work was accomplished in filed conditions following a randomized complete block design with six treatments and four replications. The treatments consisted of two pre-emergent herbicides: alachlor and trifluralin, two post-emergence: fenoxaprop-p-ethyl and sethoxydim and two checks (with and without weeding). Crop cycle, flowering initial, plant height, stem diameter, achenes physiologically mature, chapters diameter, broken plants number, lodged plants number, final stand and achenes yield were evaluated. Based on the obtained results, it was possible to conclude that herbicides that showed higher toxicity to sunflower plants were: imazaquin, metribuzin, chlorimuron-ethyl, [fomesafen + fluazifop-p], imazapyr and imazethapyr. The pre emergent herbicides alachlor, trifluralin, fenoxaprop-p-ethyl and sethoxydim were selective to sunflower crop. Fenoxaprop-p-ethyl herbicide may be used in a program of weeds integrated management in sunflower crop, because only trifluralin, alachlor and sethoxydim herbicides are registered for this crop in Brazil.Os experimentos foram instalados em Prudente de Morais, MG, em 2010 e 2011, com o objetivo de avaliar a seletividade e a eficácia de herbicidas aplicados em pré e pós-emergência na cultura do girassol, bem como de estudar a dinâmica populacional de plantas daninhas. O trabalho de 2010 foi conduzido em casa de vegetação em delineamento em blocos ao acaso com 11 tratamentos e três repetições. Os tratamentos foram constituídos por dez herbicidas, sendo quatro pré-emergentes e seis pós-emergentes (alachlor, imazaquin, metribuzin, trifluralin, chlorimuron-ethyl, fenoxaprop-p-ethyl, [fluazifop-p + fomesafen], imazapyr, imazethapyr e sethoxydim) e uma testemunha. Foram avaliados os efeitos fitotóxicos, altura das plantas, número de folhas e a biomassa seca da parte aérea e raízes aos 60 dias após a aplicação. Em 2011 o trabalho foi conduzido a campo, em delineamento de blocos ao acaso com seis tratamentos e quatro repetições. Os tratamentos consistiram dos herbicidas alachlor e trifluralin (pré-emergência), fenoxaprop-p-ethyl e sethoxydim (pós-emergência) e duas testemunhas (capinada e sem capina). Foram avaliados o ciclo da cultura, o início de florescimento, a altura de plantas, o diâmetro do caule, a maturação fisiológica dos aquênios, o diâmetro de capítulos, o número de plantas quebradas, o número de plantas acamadas, o estande final e o rendimento de aquênios. Com base nos resultados pode-se concluir que os herbicidas que apresentaram maior fitotoxicidade ao girassol foram: imazaquin, metribuzin, chlorimuron-ethyl, [fluazifop-p + fomesafen], imazapyr e imazethapyr. Os herbicidas pré-emergentes alachlor e trifluralin, e os pós-emergentes fenoxaprop-p-ethyl e sethoxydim mostraram-se seletivos para o girassol. O fenoxaprop-p-ethyl poderá vir a ser utilizado em um programa de manejo integrado de plantas daninhas no girassol, pois apenas trifluralin, alachlor e sethoxydim são herbicidas registrados para esta cultura

Avaliação de cultivares de alfafa nas condições de Cerrado no Estado de Minas Gerais

The objective of this work was to evaluate the yields of alfalfa cultivars in the Cerrado region of Minas Gerais State, Brazil. A randomized block design with three replications was used. During the dry and rainy season, significant differences were observed among cultivars for forage production, crude protein content, leaf:stem ratio, insect and disease resistance. The Crioula and P 30 cultivars had the best performance for forage production and resistance to insects and diseases. These cultivars are recommended for forage production in the Cerrado region of the Metallurgic Zone of Minas Gerais State.O objetivo deste trabalho foi avaliar o potencial forrageiro de cultivares de alfafa na região de Cerrado do Estado de Minas Gerais. O delineamento experimental foi o de blocos ao acaso, com três repetições. Durante os períodos de seca e das águas, foram observadas diferenças significativas entre as cultivares quanto ao potencial de produção de forragem, teor de proteína bruta, relação folha/caule e tolerância a pragas e doenças. As cultivares Crioula e P 30 destacam-se das demais em relação ao potencial produtivo e resistência a pragas e doenças e são recomendadas para a região dos Cerrados da Zona Metalúrgica de Minas Gerais

Adubação nitrogenada na produção e composição química do capimbraquiária sob pastejo rotacionado

A produção de forragem de melhor qualidade pode ser obtida pela mudança no método de pastejo, de contínuo para rotacionado, associada à prática da adubação, especialmente a nitrogenada. Avaliou-se nas estações chuvosas dos anos 2002/2003 e 2003/2004 o efeito de doses de nitrogênio, N (0, 100, 200 e 300 kg ha-1), na produção de matéria seca e na composição bromatológica (FDA, FDN, hemicelulose, celulose, lignina e proteína bruta) de uma pastagem de capim-braquiária (Urochroa decumbens cv. Basilisk) manejada em pastejo rotacionado. Além disso, foram avaliadas as eficiências de duas fontes de nitrogênio (sulfato de amônio e ureia) e de recuperação do nitrogênio pela pastagem. As doses de nitrogênio, como ureia no primeiro ano e ureia e sulfato de amônio no segundo ano, foram parceladas em aplicações iguais durante a estação chuvosa. Efeitos lineares foram observados para a produção de matéria seca (MS) e o teor de proteína bruta em resposta ao nitrogênio aplicado. Valores da ordem de 18 e 14 kg MS/kg N aplicado foram obtidos no primeiro e segundo ano respectivamente. Para proteína bruta, teores de 9,1 e 11,7% foram observados com a aplicação de 300 kg ha-1 de N, no primeiro e segundo ano, respectivamente, enquanto para a testemunha (0 kg ha-1 de N), os teores encontrados foram 6,6 para o primeiro ano e 7,1% para o segundo ano. Por sua vez, os teores de FDN, FDA, hemicelulose, celulose e lignina não foram afetados pelas doses de nitrogênio. As fontes ureia e sulfato de amônio não diferiram entre si. As eficiências de recuperação de nitrogênio na matéria seca disponível foram de 33,1; 41,7; e 42,2% em resposta às doses 100, 200 e 300 kg ha-1 N, respectivamente, que podem ser consideradas relativamente baixas.Production of better quality forage can be achieved by changing grazing method, from continuous grazing by rotational grazing, associated with fertilization practices, especially nitrogen fertilization. It was evaluated during the rainy seasons of 2002/03 and 2003/04 the effect of nitrogen doses (0, 100, 200 and 300 kg ha-1) on dry matter yield and on chemical composition (crude protein, ADF, NDF, hemicellulose, cellulose and lignin) of a Urochroa decumbens cv. Basilisk pasture, managed under rotational grazing. In addition, it was evaluated the efficiencies of two nitrogen sources (ammonium sulfate and urea) and recovery of nitrogen by the pastures. The nitrogen doses, as urea in the first year and ammonium sulfate and urea in the second year, were split in equal applications during the rainy season. Linear effects were found to dry matter (DM) yield and crude protein content in response to the nitrogen applied. Values of 18 and 14 kg DM/kg N applied were obtained in the first and second year, respectively. For crude protein, contents of 9.1 and 11.7% were noted with the application of 300 kg ha-1 N, in the first and second year respectively, whereas in the control treatment (0 kg ha-1 N), the contents found were 6.6% for the first year and 7.1% for the second year. In turn, contents of NDF, ADF, hemicellulose, cellulose and lignin were not affected by nitrogen doses. Sources of urea and ammonium sulfate did not differ from each other. Efficiencies of nitrogen recovery in available dry matter were 33.1, 41.7 and 42.2% in response to 100, 200 and 300 kg ha-1 N, respectively, which can be considered relatively low

PRODUTIVIDADE ECONÔMICAE COMPONENTES DA PRODUÇÃO DE ESPIGAS VERDES DE MILHO EM FUNÇÃO DAADUBAÇÃO NITROGENADA

The effect of nitrogen (N) doses on yield of the green maize ears and its production components was evaluated during two years. Five N doses (0, 60, 120, 180 and 240 kg ha-1) applied in topdressing were tested in a randomized block design with four replications. The efficiency of treatments was evaluated by the production and the number of commercial green ears per hectare, weight of husked and unhusked ears, length and diameter of unhusked ears and husked ear/husk ratio. Increases in husked commercial ear yield by N application were found, with maximum production of 13.52 t ha-1 estimated by 157 kg ha-1 N application (first year) and of 14,86 t ha-1 with 177 kg ha-1 N dose (second year). The increases in the production of green ears were not due to increases in the number of ears per area and by length of these. Differently of husked ear/husk ratio, the average weights of the husked and unhusked ears and diameter of unhusked ears were affected by N application. It was proposed a table of recommended N doses based on pre-establishedprices of N and commercial ears

Avaliação de cultivares de alfafa nas condições de Cerrado no Estado de Minas Gerais Performance of alfalfa cultivars in the Cerrado ecosystem of Minas Gerais State, Brazil

O objetivo deste trabalho foi avaliar o potencial forrageiro de cultivares de alfafa na região de Cerrado do Estado de Minas Gerais. Odelineamento experimental foi o de blocos ao acaso, com três repetições. Durante os períodos de seca e das águas, foram observadas diferenças significativas entre as cultivares quanto ao potencial de produção de forragem, teor de proteína bruta, relação folha/caule e tolerância a pragas e doenças. As cultivares Crioula e P 30 destacam-se das demais em relação ao potencial produtivo e resistência a pragas e doenças e são recomendadas para a região dos Cerrados da Zona Metalúrgica de Minas Gerais.The objective of this work was to evaluate the yields of alfalfa cultivars in the Cerrado region of Minas Gerais State, Brazil. A randomized block design with three replications was used. During the dry and rainy season, significant differences were observed among cultivars for forage production, crude protein content, leaf:stem ratio, insect and disease resistance. The Crioula and P 30 cultivars had the best performance for forage production and resistance to insects and diseases. These cultivars are recommended for forage production in the Cerrado region of the Metallurgic Zone of Minas Gerais State

Production and nutrition of irrigated Tanzania guinea grass in response to nitrogen fertilization

The objective of this study was to evaluate the effects of nitrogen (N) fertilization in the four seasons of the year on forage production, nitrate (NO3) in the sap, total N in the forage and relative chlorophyll index (SPAD reading) in the leaves of irrigated Panicum maximum cv. Tanzania grass, establishing their critical ranges. In addition, we evaluated the ability to predict forage production based on NO3 in the sap, total N in the forage and relative chlorophyll index. The soil in the experimental area was classified as an Oxisol (Red-Yellow Latosol) with a clayey texture. Annual rates of N (0, 200, 400 and 800 kg ha-1) in the form of urea were the treatments tested. Irrigation was performed through a conventional spray system. The NO3 content in the sap and the relative chlorophyll index were measured in leaves using a portable meter with NO3 selective electrode and the SPAD-502 portable chlorophyll meter device, respectively. Tanzania guinea grass was very responsive to N fertilization, except in the winter. The critical ranges of the SPAD reading proved to be more adequate for monitoring the nutritional state of N of Tanzania guinea grass in the different seasons of the year than the NO3content in the sap and the total N content in the dry matter. Use of the chlorophyll meter is more advantageous than the use of the portable meter with an nitrate selective electrode for predicting the nutritional status of Tanzania guinea grass